The present invention relates to resolvers. Resolvers are used to determine the rotational position and/or rotational speed of a rotating part such as a shaft.
For example, electric machines which are employed as traction motors and generators in hybrid vehicles often employ variable reluctance resolvers to determine the rotational position and speed of the electric machine and thereby provide the precise control necessary to operate the electric machine in cooperation with the other vehicle systems.
Variable reluctance resolvers typically include a stator with a plurality of salient poles and windings mounted thereon and a rotor in which the stator induces a magnetic flux. The rotor typically has an outer perimeter which defines a wave form and, thus, also defines a variable air gap between the resolver rotor and the resolver stator. The magnetic flux induced by the interaction of the resolver rotor and stator and the changes therein due to the rotation of the resolver rotor allows the rotational speed and position of the resolver rotor to be determined as is well-known to those having ordinary skill in the art.
Excessive electromagnetic interference (“EMI”) can interfere with the operation of such variable reluctance resolvers and have a negative impact on their performance.